The present invention arises in the operation of typical large paper manufacturing facilities located in cold climate areas such as Canada, Scandanavia, and Siberia. A larger paper plant has pulping, digesting, pulp dryer, and paper machine facilities which are frequently housed in separate buildings at some distance apart. There are such sources of waste heat as heated air collected over the paper machine driers, exhaust steam from the steam heated rolls of the paper machine, heated air from the pulp drier, exhaust steam from the pulp drier, heat from vacuum pumps serving driers, heated exhaust gases discharged by vacuum pumps, steam exhaust from thermomechanical pulping equipment, and exhaust from the digesters. Thus, there are many sources of waste heat invested in gaseous media available for distribution to heat consuming locations frequently at a distance. However, transporting heat by gaseous media is expensive because of the large bulky duct work and associated insulating materials needed to channel gaseous material in frigid weather. It is now appreciated that liquid carriers require much less expensive duct systems in constructing the rambling heat distribution systems necessary.
In a typical construction of gas-to-liquid heat exchangers, liquid is passed through a large plurality of parallel tubes within a chamber through which the gas is passed into contact with the outer surfaces of the tubes. If in any emergency the gas channel of an endothermic is subjected to ambient temperatures of the winter season, such a heat exchanger is subject to freeze-up which damages the tubes. Freeze-ups are particularly a hazard of the heat exchangers which are intended to heat the ambient air.
It is an essential object of the invention to provide suitable apparatus for reclaiming heat from waste industrial plant gases and transferring the heat by liquid medium to locations in dispersed relation with the sources of waste heat, and especially to provide gas-to-liquid heat exchanger apparatus resistant to freeze-ups and, if frozen, designed to remain partly open.
Another object is to provide liquid-to-gas heat exchangers which function to heat ambient air in cold climates and are capable of sustaining freeze-ups without damage.
A further object is to provide a system of reclaiming and collecting heat energy, and redistributing the energy to dispersed heat consumption locations through the use of freeze-damage immune heat exchangers.